找不到按钮点击事件?

Q: Am I crazy? I've got the event. The name's copy/pasted so I know it's no typo. What am I missing here? (Don't worry about parameters, please, this is for training and I've been told not to use them at this time)

      <asp:UpdatePanel ID="UdpEPL" runat="server" UpdateMode="Conditional" Visible="False">
            <Triggers>
                <asp:AsyncPostBackTrigger ControlID="BtnEpl" EventName="BtnEpl_Click" />
            </Triggers>
      <ContentTemplate> 

      <!--some label and textbox controls-->

      <br />
      <asp:Button ID="BtnEpl" runat="server" Text="Submit" AutoPostBack="True" 
                    onclick="BtnEpl_Click" />
      <br />

      <!--the second update panel-->

         <asp:UpdatePanel ID="UdpEplShow" runat="server" UpdateMode="Conditional" Visible="False">
                  <Triggers>
                           <asp:AsyncPostBackTrigger ControlID="BtnEpl" EventName="BtnEpl_Click" />
                  </Triggers>
         <ContentTemplate>      
      <!--more labels displaying the user input from the first update panel-->

The codebehind:

 protected void BtnEpl_Click(object sender, EventArgs e)
        {
             string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
            string EplQuery = "INSERT INTO EPL (Entity, Employees, CA, MI, NY, NJ, Primex, EplLim, EplSir, Premium, Wage, Sublim) VALUES ('" + TbEplEntity + "', '" + TbEplTotalEmpl + "', '" + TbEplCalEmpl + "', '" + TbEplMichEmpl + "', '" + TbEplNyEmpl + "', '" + TbEplNjEmpl + "', '" + TbEplPrimEx + "', '" + TbEplLim + "', '" + TbEplEplSir + "', '" + TbEplPrem + "', '" + TbEplWage + "', '" + TbEplInvestCost + "')";
            string EplIdQuery = "SELECT SCOPE_IDENTITY() AS LastInsertedInstanceId";

        using (SqlConnection EplConn = new SqlConnection(connectionString))
        {
            EplConn.Open();
            SqlCommand EplCmd = new SqlCommand(EplQuery, EplConn);
            SqlCommand EplIdCmd = new SqlCommand(EplIdQuery, EplConn);
            using (EplCmd)
            using (EplIdCmd)
            {
                EplCmd.ExecuteNonQuery();
                SqlDataReader EplDr = EplIdCmd.ExecuteReader();
                EplDr.Read();
                int lastInsertedInstanceId = Convert.ToInt32(EplDr[0]);


            }

            string x = Request.QueryString["InstanceId"];
            string EplShowQuery = "SELECT Entity, Employees, CA, MI, NY, NJ, Primex, EplLim, EplSir, Premium, Wage, Sublim FROM EPL WHERE InstanceId =" + x;
            using (SqlCommand EplShowCmd = new SqlCommand(EplShowQuery, EplConn))
            {
                SqlDataReader EplDr = EplShowCmd.ExecuteReader();
                EplDr.Read();
                LblEplShowEntity.Text = EplDr.GetString(0);
                LblEplShowTotalEmpl.Text = EplDr.GetInt32(1).ToString();
                LblEplShowCalEmpl.Text = EplDr.GetInt32(2).ToString();
                LblEplShowMichEmpl.Text = EplDr.GetInt32(3).ToString();
                LblEplShowNyEmpl.Text = EplDr.GetInt32(4).ToString();
                LblEplShowNjEmpl.Text = EplDr.GetInt32(5).ToString();
                LblEplShowPrimEx.Text = EplDr.GetInt32(6).ToString();
                LblEplShowLim.Text = EplDr.GetInt32(7).ToString();
                LblEplShowSir.Text = EplDr.GetInt32(8).ToString();
                LblEplShowPrem.Text = EplDr.GetInt32(9).ToString();
                LblEplShowWage.Text = EplDr.GetInt32(10).ToString();
                LblEplShowInvestCost.Text = EplDr.GetInt32(11).ToString();

            }
        }
            UdpEPL.Visible = false;
            UdpEplShow.Visible = true;


    }
}

In trigger, you only need to specify event Name.

It should be

<asp:AsyncPostBackTrigger ControlID="BtnEpl" EventName="Click" />

instead

<asp:AsyncPostBackTrigger ControlID="BtnEpl" EventName="BtnEpl_Click" />

Are you closing the First ContentTemplate at some point? In case you do it after the Button Markup please enable ChildrenAsTriggers="true".

Just in the interest of giving this question an answer, I must point out my mistake. @Muhammad asked me why the panels were set to visible=false; this was because of the way I tried to approach the page structure. I wanted to use ajax to display input forms, and then hide them upon submission to the db and display the data in read-only format, so I thought I'd put both forms in update panels and make them invisible until they were called by the dropdownlist. Unfortunately what I discovered is that triggers won't fire on invisible controls. Don't quote me, but as I understand it, this is because invisible server side controls don't send markup to the browser. Lesson learned.